Synthesis And Application Of New Photocatalyst For Wastewater Treatment

It is hard for dyes to be degraded, and these dyes have brought much pollution to water. The study on the treatment of waste water containing dyes have been received much attention recently. Among the water treatment technologies, the photocatalytic oxidation has drawn widely attention for its environment-friendly, high efficient and energy saving. This paper introduce heterogeneous photocatalytic oxidation technology and the dealt with waste water technique, and utilize this new technology for analyzing and researching the decomposing dye in waste water.The vanadate is a kind of photocatalyst with great potential, it has been reported that BiVO₄, InVO₄, Ag3VO₄ have a very narrow band gap, enabling the full utilization of solar to degrade pollutants. In this thesis, La(NO3)3·6H2O and NaVO3·2H2O were used as raw materials to obtain La_1-xFe_xVO₄ (x = 0, 0.05, 0.10, 0.20) and LaFeO3. The samples were characterized with X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-visible absorption spectra (UV-Vis) respectively. Finally, the photocatalytic degradation was carried out by using LaVO₄ nanoparticles as photocatalyst and Rhodamine B as dye wastewater. The effects of the different photocatalysts, the pH value and the dosage of the photocatalyst on photodegradation were studied. Moreover, the LaVO₄ photocatalytic mechanism was also proposed, Results were as following:(1) Well-crystallized LaVO₄ nanoparticles can be easily prepared in a molten salt medium. The effect of calcining temperature and the salt amount on the crystallization and development of LaVO₄ phase was initially investigated. At 270°C, spherical LaVO₄ nanoparticles with ca.20nm in diameter can be formed, companying with a small amount of nano-sheets. Beyond that temperature (e.g.340°C, 400°C), only can well-crystallized nanoparticles be obtained, and grow up with the calcining temperature. The presence of the molten salt medium would inhibit the formation of nano-sheets and promote the crystallization and development of LaVO₄ nanoparticles. UV-Vis absorption spectra confirm their excellent optical properties.(2) Nanocrystalline La_1-xFe_xVO₄ (x = 0, 0.05, 0.10, 0.20) solid solution powders were successfully synthesized via a low-temperature molten salt method. The results show a gradual phase transformation from monoclinic to tetragonal-phase with the increase of x value, accompanied by a remarkable morphology variation from nearly-spherical nanoparticles to nanorods, nanosheets. Fe³⁺ doped LaVO₄ can be fully stabilized in tetragonal-phase at x = 0.20, whereas only a monoclinic-phase can be obtained without adding Fe³⁺.(3) The experiment of single-factor was carried out to fine the best conditions for the photodegradation of rhodamine B were: La_1-xFe_xVO₄ (x = 0.20), pH value for 4, the dosage of photocatalyst for 1g/L, and the dosage of rhodamine B for 20mg/L.(4) It was predicted that the process of LaVO₄ photodegradation was under the photocatalysis and photosensitization's association action. Moreover, the photosensitization played a major role. When the two factors reached a balance, the maximum rate was presented.(5) LaFeO₃ nanoparticles can be easily prepared in a molten salt medium. The presence of the molten salt medium would promote the crystallization and development of LaFeO₃ nanoparticles. The followed photocatalytic degradation data present that the LaFeO₃ exhibits higher photocatalytic activity. Within 60min, more than 90% photodegradation rate can be achieved.